Water relations in cotton plants infected with Phymatotrichum omnivorum were studied to determine the mechanism of wilt development. Relationships between leaf water and osmotic potentials, relative water contents, and diffusive resistances of leaves from diseased and waterstressed healthy plants were similar, indicating that wilting was not due to changes in leaf osmotic regulation. Rates of recovery from wilting, measured as increases in relative water content with time in both diseased and waterstressed healthy plants were identical. There was no significant difference in root dry weight of healthy and diseased plants, indicating that wilting is not a consequence of reduced root area. Resistance to water flow in roots and lower stems increased significantly over those of healthy plants as upper leaves of diseased plants began to wilt. However, resistance to water flow in petioles of diseased plants was unchanged. These results show that wilting in cotton plants is probably the consequence of increased resistance to water flow in roots. Results of a preliminary study indicate that a high-molecular-weight substance produced by the fungus in culture may cause blockage of xylem elements in roots and lower stems and contribute to the increased resistance to water flow.

No description available.

No description available.

No description available.

Efficacy of Bacillus thuringiensis Berliner against the first three larval instars of Heliothis virescens (F.) was studied under greenhouse and field conditions. The primary objective of these studies was to determine the susceptibility of the tobacco budworm to Dipel, a commercial preparation of Bacillus thuringiensis. Both greenhouse and field studies showed that first-instar larvae were more susceptible to all dosage levels of Dipel tested (0.125, 0.25, 0.5, and 1.0 1b/A). The higher rates of 0.5 and 1.0 1b/A gave better control and remained effective for longer periods against the first-, second- and third-larval instars than did the lower rates of 0.125 and 0.25 1b/A. The efficacy of all Dipel rates decreased significantly with each subsequent post-application-date bioassay, and only the higher dosages of 0.5 and 1.0 1b/A remained effective at the three-day residue period in the field studies. The addition of a feeding stimulant, Coax, at 0.25 1b/A, to all Dipel treatments resulted in a significant increase in larval mortality of all instars tested. Dipel plus Coax exhibited longer residual activity than did Dipel alone, indicating that Coax may protect the spores and toxin from degradation by the direct sunlight. When second-instar tobacco budworm larvae were allowed to feed on Dipel-treated terminals for 6, 18 or 30 hours and then transferred to untreated diet, they showed a great capacity to recover from the effect of the toxin. However, as the Dipel rate or exposure time was increased, the ability of larvae to recover was decreased. Dipel did have an effect on the biological activity of treatment-surviving larvae. Larval and pupal development was delayed, pupal weight was decreased, and female fecundity was reduced. In all cases the changes were proportional with the Dipel rate and with the length of exposure. No apparent effect was shown relative to adult longevity or egg viability for those surviving Dipel treatments as larvae. When Dipel was applied directly on tobacco budworm eggs, it had no effect on egg hatch but did significantly affect survival of newly-emerged larvae, indicating the larvae consumed a lethal dose of the toxin during eclosion. The compatibility of Dipel in combination with Geocoris punctipes (Say) against first-instar larvae of Heliothis virescens was also studied under greenhouse and field conditions. Results of these studies indicated the possibility of utilizing the two biological agents to suppress tobacco budworm populations in the field. A minimum density of one Geocoris nymph per 4 row feet is required, plus an effective field rate of Dipel. When adult tobacco budworms were fed on Dipel at 32000 IU/ml, their longevity and fecundity were significantly reduced. An adult feeding stimulant is needed to lure the adults to a Dipel source.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

No description available.

Gossypium barbadense (Pima cotton) was planted in a naturally infested field containing 600 cfu/g of Thielaviopsis basicola on two planting dates in 1986 and in 1988 near Coolidge, AZ. Soil temperatures ranged from 18-20 C and 24-26 C at a depth of 15 cm on the first and second planting dates, respectively. During both seasons, disease incidence approached 100% with 75-100% cortical root decay 1 mo after the first planting. Two wk after the second planting, there was an 89% disease incidence in 1986 and 92% in 1988 with 50-75% cortical root decay in both instances. Plant stands were reduced by 28% in 1986 and 32% in 1988 in the first planting and 11% in 1986 and 8% in 1988 in the second planting. In October 1986, 32% and 5% of the plants in the first and second plantings, respectively, had darkened stelar root tissues near the crown that contained hyphae and aleuriospores of T. basicola. G. hirsutum was grown at 20 and 28 C in a growth chamber in soils containing 0, 90, and 600 cfu/g of T. basicola. Seedling stunting and cortical decay increased with inoculum density at both temperatures but were more severe at 20 C. SEM demonstrated that phialoconidia and aleuriospores germinated, produced appressoria, and penetrated within 12 and 48 hr, respectively. Five days after inoculation infected cells were filled with hyphae and aleuriospores. Populations of T. basicola in the test field, in 1986 after 4 yr of planting cotton, were 596, 481, and 142 cfu/g 1, 2, and 7 mo after planting. During 1987 the field was split into two plots. One was planted with wheat and the other was fallowed. In 1987 populations of T. basicola remained stable. In 1988 disease incidence and populations of T. basicola were monitored in the wheat and fallow plots currently planted with Pima cotton. In February 1988 soil populations of T. basicola dropped to 87 cfu/g and 13 cfu/g in the wheat and fallow treatments, respectively. However, in April 1988, 1 mo after planting, Pima cotton growing in the wheat rotation plot had a disease incidence of 71% with an average cortical decay of 47%. In contrast, cotton planted in the fallow treatment had a disease incidence of 43% with an average cortical decay of 23%. At this time populations of T. basicola were 50 and 10 cfu/g in the wheat and fallow treatments, respectively.

Phymatotrichum root rot is a fungal disease with a host range that includes many economically important crops in the southwestern United States and Mexico. While it has been studied since the late nineteenth century, ecological relationships of the disease, particularly those related to its distribution and dispersal, are not understood. Combined ground radiance sampling and aerial photographic interpretation was employed to study the distribution of Phymatotrichum root rot in cotton. Radiometric ground sampling showed that diseased cotton has a characteristic spectral signature that is significantly different from healthy cotton at visible wavelengths. Micro-scale examination of distribution within fields utilized multitemporal photography, both within season (1983) and for four seasons (1979-1982), revealed that the disease spreads during a season, but is not recurrent in many cases between years. Meso-scale mapping employed multitemporal photography to map distribution during a four-year period. When compared to mapped soil units, these data revealed a significantly non-random relationship between the diseased areas of fields and fine-textured soil units that may be based on moisture-holding potential. A yield analysis was also preformed using Thematic Mapper Simulator data and computer analysis.